Is Acceptable Noise Level Affected by the Number of Competitive Talkers? An Implication of Informational Masking and Listening in Dips for Acceptable Noise Level Mechanism

Background and Aim: The Acceptable Noise Level (ANL), which is an effective  clinical tool for quantitative assessment of noise tolerance, is affected by some known variables related to both subject and testing materials. The present study examined how the characteristics of different babble noises may affect the ANL results in normal adult listeners. Methods: Forty Persian listeners with normal hearing participated. In addition to typical ANL testing with 12-talker noise, the ANL was obtained in 8 different conditions varying in number of talkers from 2 to 10 in the babble noises presenting forward and backward. Results: There was a significantly lower ANL for 2-talker babble compared to 4, 8, 10, and 12-talker babble in both forward and backward noise conditions. With the increase in talkers in noise, the ANL becomes worse but reaches almost a plateau with more than 4 talkers in babble noise. There was a statistically significant difference between 2-talker forward and 2-talker backward noises, with no difference for the other conditions. Conclusion: This finding that the ANL is affected by the number of talkers in babble noise and by the forward and backward background noise suggests that informational masking and listening in dip mechanisms are involved in ANL for normal hearing people at least. Keywords: Acceptable noise level; speech babble noise; listening in dips; informational masking; energetic masking